1. Field of the Invention
This invention relates generally to metal-organic framework-based molecular sieves for selective gas adsorption and particularly to such sieves which provide thermally-dynamic pore sizes which are continuously adjustable.
2. Description of the Related Art
Gas separation is an important operation in many industries and conventional processes include distillation, absorption, and molecular sieves. However, using such processes to separate, for example, mixtures comprising chemical pairs of similarly-sized molecules or those with similar boiling points such as ethylene and propylene, methane and ethylene, nitrogen and methane, nitrogen and oxygen, hydrogen and carbon monoxide, and hydrogen and nitrogen can be difficult.
Recently, metal-organic frameworks (MOFs) have been utilized to produce porous materials suitable as molecular sieves for adsorbing specific molecular species. Such frameworks, which comprise metal clusters linked together in a reticular structure with linking ligands, can provide predetermined pore size and functionality. However, when the size disparity of the gas pairs to be separated is small, a molecular sieve with the optimum pore size is not always readily available and a mismatch inevitably leads to an inefficient operation. Furthermore, the pore size of even MOFs is fixed upon activation. Therefore, the need exists for a molecular sieve capable of dynamically providing a continuum of pore sizes. Particularly, the need exists for a molecular sieve having a continuum of pore sizes in the range of most commercially important gas separations.